Tennis rackets in the prior art weigh from 12 ounces for a light racket to over 14 ounces for a heavy racket. The center of percussion or sweet spot ranges from 17 inches to 18.50 inches, from the end of the racket handle. This center does not coincide with the center of the strings, but is closer to the handle end. Thus, when a ball is struck at the center of the racket face, a shock is felt at the handle grip. Because the prior art rackets are more flexible than is desired, vibrations are set up in the frame which robs energy from the rebound of the ball and causes vibrations to be transmitted to the arm of the player, as well as cause inaccuracy in the rebound of the ball. The weight of the prior art rackets contributes heavily to the development of tennis elbow, as well as the fatigue of the player's arm and body.
Further, rackets of the past have utilized wood, aluminum, steel,fiberglass, boron and graphite composites.
The prior art, while utilizing these materials, have not utilized the structural configurations to take advantage of the stiffness to unit weight ratio, as well as the strength to unit weight ratio of these materials to obtain a reduction in weight, increase the center of percussion, reduce the deflection, reduce the vibration, and yet maintain the same swing weight.
It is noted that in U.S. Pat. No. 1,539,019, by Nikonow, an attempt was made to reduce the weight of the racket, increase the distance of the center of percussion from the handle end, by increasing the distance of center of gravity or balance point further from the handle end. He states he attained a weight of 12 ounces, a center of balance of between 15 to 17 inches. The overall length of the racket was 26 inches and the striking power was equivalent to a 141/2 ounce racket. This racket was made of wood and the crossectional areas shown were not the best to achieve the results desired.
Another difficulty with the prior art is that when balls are hit which are to the left or right of a line running from the tip of the racket to the handle down the center, henceforth called the longitudinal axis of the racket, the racket tends to turn in hand of the player causing a poorly hit ball with little power or accuracy.
Another difficulty with the prior art rackets is that they are rated as light, medium and heavy, but very little is said about the swing weight of a racket. This swing weight is the important parameter in determining the striking power of a racket. For example, in a set of golf clubs, the swing weight of all the clubs are substantially the same, and sets may be obtained in combination of categories A,B,C,D and 1,2,3,4, providing for 16 graduations of swing weight for a user to choose from. This swing weight is the moment of inertia about a point 2.25 inches above the end of the club handle (see U.S. Pat. No. 3,473,370 by E. J. Marciniak.).
Further, the prior art does not provide for easily available means for measuring the moment of inertia of a racket.
Further, the prior art does not provide for an analysis to determine the proper moment of inertia to be used, considering the weight of a tennis ball, the velocity of the on-coming ball with respect to the player.
Another difficulty with the prior art rackets is that the force necessary to deflect the strings a given amount perpendicular to the face of the racket varies considerably from the center .[.of.]. .Iadd.to .Iaddend.the edges, in part because of the smaller length of the strings at the edges from those used at the center. This variation contributes further to inaccurate hits.